The second trimester of pregnancy lasts about 15 weeks, running from week 13 through the end of week 27. It falls roughly in the middle of a full-term pregnancy and is often considered the most comfortable stretch, as early symptoms like nausea tend to fade while the physical demands of the third trimester haven’t yet set in.
When It Starts and Ends
Your second trimester begins at the start of week 13 and wraps up at the end of week 27. That works out to about three and a half months, covering the fourth, fifth, and sixth months of pregnancy. Keep in mind that pregnancy weeks are counted from the first day of your last menstrual period, not from conception, so you’ve actually been pregnant for roughly 11 weeks at the start of the second trimester and about 25 weeks at the end of it.
What You’ll Feel During These Weeks
For many people, the second trimester brings a noticeable energy boost. The fatigue and morning sickness that define the first trimester often ease up as the placenta takes over hormone production. Your belly becomes visibly larger, and you’ll likely start feeling your baby move for the first time, a sensation called quickening. First-time parents typically notice movement between 20 and 24 weeks, while those who’ve been pregnant before may feel it as early as 16 weeks.
Weight gain picks up during this period. If you started pregnancy at a healthy weight, the general guideline is to gain about 1 pound per week through the second and third trimesters. If you started at a higher weight, roughly half a pound per week is the typical target. These are averages, and individual variation is normal.
How Your Baby Develops Week by Week
The second trimester is when your baby transforms from a small, largely unrecognizable form into something that looks unmistakably human. The changes are rapid and dramatic.
In the early weeks (13 to 16), bones begin to harden in the skull, arms, and legs. Red blood cells start forming in the spleen, the scalp hair pattern takes shape, and the eyes begin to move slowly. By week 16, the ears are nearly in their final position on the head.
The middle stretch (17 to 22) brings a wave of sensory and physical development. Toenails start growing around week 17. By week 18, the ears stand out from the head and the baby may begin hearing sounds for the first time. The digestive system starts working. A protective waxy coating covers the skin to shield it from the amniotic fluid. Around week 20, your baby settles into regular sleep-wake cycles and can be woken up by noise or your movements. By week 21, fine downy hair covers the entire body, and the sucking reflex develops. Eyebrows and hair become visible around week 22, and the reproductive organs are formed.
In the final weeks (23 to 27), the baby’s lungs begin producing a substance that will eventually let them inflate properly at birth. Rapid eye movements start, fingerprint and footprint patterns form, and by week 25 your baby may respond to familiar sounds like your voice. Eyebrows and eyelashes are fully formed by week 26, though the eyes may not open until around week 28.
Key Screenings and Tests
Two important medical screenings happen during the second trimester. The anatomy scan, a detailed ultrasound that checks your baby’s organs, bones, and growth, is performed between 18 and 22 weeks. This is the appointment where many parents learn the baby’s sex, and where your provider looks closely at the heart, brain, spine, and other structures.
Later in the trimester, between 24 and 28 weeks, you’ll be screened for gestational diabetes. This involves drinking a sugary solution and having your blood drawn to see how your body processes the sugar. If the initial screen comes back high, a longer follow-up test confirms or rules out the diagnosis.
Why It’s Called the “Easiest” Trimester
The second trimester has a reputation as the sweet spot of pregnancy, and there’s a biological reason for that. By week 13, hormone levels stabilize in a way that reduces nausea for most people. At the same time, you’re not yet large enough for the back pain, breathlessness, and sleep difficulties that characterize the third trimester. Energy levels rebound, appetite returns, and many people find this the most productive and comfortable phase of pregnancy. That said, new symptoms can appear: round ligament pain from your expanding uterus, nasal congestion from increased blood flow, and skin changes like a dark line down the center of the abdomen are all common.